In modern automatic milking farms vacuum pumps supply vacuum to the milking machine for performing necessary tasks, such as milking and cleaning.
In robot milking each milking station has conventionally been equipped with its own dedicated vacuum pump. In milking farms using many milking stations this is not an optimal solution and various solutions has been suggested for using a common vacuum source arrangement for supplying vacuum to a plurality of milking stations.
In larger automatic robotic milking farms two or more automatic milking stations may be serving a herd of milking animals. The automatic milking stations will then have a common total vacuum requirement, for which the vacuum pumps need to be dimensioned. Furthermore, such milking machines operate in different operating modes, such as milking, teat cleaning, milking machine cleaning, and stand-by to mention a few. Each of these modes has individual vacuum requirements, wherein for instance during cleaning of the milking machine a high air flow may occur, whereupon the vacuum level drops, whereas during milking a steady high vacuum level is required. Thus, the vacuum pumps need to be dimensioned to handle a situation where all milking machines are in the worst operating mode for vacuum supplying purposes. Milking machine cleaning may in turn include a number of different cleaning steps, such as cleaning of teat cups, cleaning of teat cleaning cups, cleaning of conduits, pre-rinsing, cleaning, post-rinsing, drying, etc. Milking machine cleaning may typically be divided into a short rinsing of teat cups and conduits, which may be conducted between the milking of each animal, and cleaning of the entire milking machine, which might be performed only once, twice or three times a day.
Assuming for instance that milking machine cleaning may result in such a high air flow as 500 litres/minute, during which the vacuum level may drop to approximately 30 kPa, and that milking requires a steady vacuum of 45 kPa and may result in air-flows of 150 liters/minute. Then, for a system comprising two milking machines being served by one single vacuum pump, the pump needs to be dimensioned to provide a steady vacuum of 45 kPa at an air flow of 650 liters/minute but also to provide an approximate vacuum level of 30 kPa at an air flow of 1000 liters/minute.
However, milking machine cleaning is only occasionally performed at both the milking machines at the same time, but typically different tasks are performing at the milking machines, where one may be less requiring for the vacuum pump. Thus, the vacuum pump has typically to be dimensioned for a situation, which will not occur very often. A vacuum pump dimensioned accordingly will of course be expensive both in purchase and in operation.
In very large farms with a large number of milking machines, where each milking machine is supplied with vacuum from a common vacuum source arrangement it is not economically feasible to dimension the common vacuum source arrangement for the worst possible situation, for instance the situation where nine milking machines are cleaned, causing high air flows into the vacuum system, while one milking machine is used for milking requiring a steady high vacuum level.
EP 1 369 033 discloses a milking system comprising a common vacuum source arrangement and a common ring line, to which at least two milking robots are connected. The common ring line has a first vacuum level and the individual milking robots have a second lower vacuum level controlled by a control means and a valve.